A Labour supporter on the campaign trail requested a public inauguration with music by Wellington band Fat Freddy's Drop and new Prime Minister Jacinda Ardern delivered.

Arriving back at Parliament yesterday afternoon after being sworn in by Governor-General Dame Patsy Reddy, Ms Ardern was mobbed by a crowd of about 1000 cheering and chanting her name, and music by a four-piece band calling themselves the Stardust Stompers, fronted by Joe Lindsay, also a member of Fat Freddy's Drop.

"I think she's great, and I think it's going to be great for New Zealand,'' Lindsay said.

It was the celebration Labour had been waiting nine years to hold.

Just a few hours earlier, a more sombre crowd of about 40 staff cheered Bill English as he made his way to Government House to formally hand in his resignation, accompanied by his wife Mary and youngest son Xavier.

Standing alongside her new Cabinet, Ms Ardern told the crowd she knew not everyone voted for her Government but it would represent them anyway.

"We will be an active government, we will be a strong government, we will be an empathetic government, we will be a government that works together,'' she said, echoing her words at Government House.

Ms Ardern's swearing-in ceremony was attended by her partner, Clarke Gayford, and her father, Ross, New Zealand's High Commissioner to Niue.

Her mother, Laurell, was attending the birth of her second grandchild. Ms Ardern's sister, Louise, gave birth to a boy in London.

Dunedin North MP David Clark and Dunedin South MP Clare Curran were also sworn in as ministers yesterday.

Labour's Cabinet met for the first time yesterday afternoon and will meet again on Tuesday, after which the updated version of its 100-day plan will be revealed.

It will include legislation to ban foreigners buying existing houses in New Zealand and legislation to allow one free year of tertiary education starting next year, the first step in Labour's larger plan for three years' free tertiary education.

"Some of our 100-day commitments we really need to act quickly on if we are to get the legislation through in time,'' Ms Ardern said.

A focus in coming days will be the Trans Pacific Partnership, which is expected to feature heavily in Ms Ardern's meetings when she attends the Apec Summit in Vietnam early next month.

She will be joined on that trip by Foreign Affairs Minister Winston Peters and Trade Minister David Parker.

"For us a priority, regardless of whether it's TPP or any other agreement, is making sure we have the ability to ban foreign buyers from buying existing homes in New Zealand,'' she said.

The previous National Government backed moving quickly on the new TPP-11 agreement and had strong support from newly re-elected Japanese Prime Minister, Shinzo Abe.

Between Labour, coalition partner NZ First and confidence and supply supporter the Green Party there are 31 Cabinet ministers, ministers outside Cabinet and under-secretaries.

Only five have been in government before: Mr Peters, Mr Parker, Nanaia Mahuta, Damien O'Connor and Shane Jones.